Capital-income breeding in wild boar: a comparison between two sexes

Abstract

Organisms differ in the strategy adopted to fuel reproduction by using resources either previously acquired and stored in body reserves (capital breeding) or, conversely, acquired during their reproductive activity (income breeding). The choice of one or the other strategy is related to several internal and external factors which are counteractive in wild boar. Based on a large dataset of culled wild boar, we investigated individual body weight variability throughout the period of 1st September–31st January, which included the main part of the mating season, among different sex and age classes to determine their position along the capital-income breeding continuum. Though food resources were abundant during the rut, adult males lost body weight suggesting they adopted a predominantly capital breeding strategy, likely owing to the high intra-sexual competition entailed by the peculiar mating system of the species. On the contrary, subadult males seemed to behave as income breeders, likely enhancing the reproductive flexibility of wild boar populations. During the rut, females stored reserves, thus suggesting that they substantially relied on them to cover future reproductive costs.

It is time to mate: population-level plasticity of wild boar reproductive timing and synchrony in a changing environment

“…This result is surprising in a heavily hunted population (i.e., subject to adult male scarcity, Fernandez-Llario and Mateos-Quesada 2003 ; Toïgo et al 2008 ) and appears in contrast with the results obtained for other ungulate species ( Milner et al 2007 ). Nonetheless, it is consistent with the findings proposed by Diefenbach et al (2019) on white tailed deer ( Odocoileus virginianus ) as well as with Brogi et al’s (2021) hypothesis regarding the flexible reproductive involvement of subadult male wild boar. As we did not consider other population traits, such as density and structure, further investigations are needed to evaluate their potential effect on wild boar temporal reproductive patterns.…”

“…Culling date and live body mass were recorded for each individual. In so doing, we included the reproductive trait mass, though it accounted only for a negligible percentage of female live body mass ( Brogi et al 2021 ). All females were aged on the basis of their tooth eruption and abrasion ( Briedermann 1990 ) and assigned to one of the following age classes: juvenile (< 1 year), subadult (between 1 and 2 years), and adult (> 2 years).…”

“…To summarize the influence of the 3 deciduous species in a single variable, we included a further global forest productivity index in the models, which we calculated following the protocol described by Bisi et al (2018) . Finally, we calculated the yearly average number of adult males per female as the number of culled adult males (>3 years; Brogi et al 2021 ) divided by the total number of adult and subadult females. We added this yearly variable as a predictor within our models to take into account the potential effects of reproductive male relative abundance on female reproductive status ( Milner et al 2007 ).…”

Atypical for northern ungulates, energy metabolism is lowest during summer in female wild boars (Sus scrofa)

“…For instance, adult males may lose body mass during the winter rut even when food supply is high. At the same time, females may even gain body mass, indicating clear differences between sexes in energy intake or -expenditure during winter 13 . Hence, we would predict that energy expenditure among males is higher during the rut leading to an even higher fall/winter peak in heart rate.…”

“…Wild boar are seasonal breeders 12 with conception events occurring from September to March 13 in central Europe, but, within this range, relatively early in the year under good environmental conditions 14 . The rut in fall/winter involves strong male competition in this polygynous species.…”